University of Crete HEP Seminars


FP7

Weak Gravity Conjecture from Unitarity

Speaker: Yuta Hamada
Institution: University of Crete
Time: Thursday 13 September 2018, 14:15
Venue: 2nd floor seminar room
Abstract: Weak Gravity Conjecture provides the lower bound on the Abelian gauge coupling in the theory of quantum gravity. In this talk, I will show that, under several assumptions, a class of weak gravity conjecture follows from the unitarity of the quantum field theory.

Novel Results from The ALICE heavy-ion experiment at CERN

Speaker: Yiota Foka
Institution: GSI and CERN
Time: Tuesday 25 September 2018, 14:15
Venue: 2nd floor seminar room
Abstract: Two-particle angular correlations were measured in pp collisions at p s = 7 TeV. The analysis was carried out for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon - baryon and anti-baryon - anti-baryon pairs, where both particles have the same baryon number, a near-side anticorrelation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.

SUSY Q and RG flows from spatially varying couplings

Speaker: Chris Rosen
Institution: Imperial College London
Time: Tuesday 6 November 2018, 14:15
Venue: 2nd floor seminar room
Abstract: Many fundamental results on the behaviour of quantum field theories along a renormalisation group flow are established under the assumption of Poincare invariant deformations. Examples of which include celebrated monotonicity properties of various "a" and "c" functions, including those related to entanglement entropy. Comparatively little is known about the properties of renormalisation group flows driven by spatially dependent couplings for relevant operators. In this talk, I report on recent progress in addressing this deficiency. Towards this end, we construct (analytically and numerically) solutions to supergravity theories holographically dual to known superconformal field theories deformed by spatially varying mass terms for fermion and boson bilinears. The associated flows can exhibit novel features such as an "RG boomerang" which returns in the IR to the same UV fixed point up to a renormalisation of length scales. The flows preserve some supersymmetry, and can be embedded in eleven dimensional supergravity. Their "top-down" holographic pedigree further allows for a precise description of the flows in terms of their dual field theory's correlation functions, the correct computation of which involves a Legendre transform of the on-shell action as required by boundary supersymmetry.

Leptogenesis via Neutrino Oscillation Magic

Speaker: Yuta Hamada
Institution: University of Crete
Time: Tuesday 13 November 2018, 14:15
Venue: 2nd floor seminar room
Abstract: The possibility of generating the baryon asymmetry of the Universe via flavor oscillation in the early Universe is discussed. After the inflation, leptons are born in some states, travel in the medium, and are eventually projected onto flavor eigenstates due to the scattering via the Yukawa interactions. By using the Lagrangian of the Standard Model with the Majorana neutrino mass terms, llHH, we follow the time evolution of the density matrices of the leptons in this very first stage of the Universe and show that the CP violation in the flavor oscillation can explain the baryon asymmetry of the Universe. In the scenario where the reheating is caused by the decay of the inflaton into the Higgs bosons, the baryon asymmetry is generated by the CP phases in the Pontecorvo-Maki-Nakagawa-Sakata matrix and thus can be tested by the low energy neutrino experiments.

Emergent gravity from hidden sectors

Speaker: Elias Kiritsis
Institution: University of Crete
Time: Tuesday 5 February 2019, 14:15
Venue: 2nd floor seminar room
Abstract: Gravitons as composite particles have been entertained since a long time, without a lot of succes. We revisit this idea motivated by the AdS/CFT correspondence. We show that hidden theories coupled to the SM may provide an emergent graviton, that is a composite of the hidden fields. This is a more general phenomenon beyond holographic theories. We explore the general setup and find that UV-sourced interactions of the stress tensor give rise to an emergent graviton in the IR. We study the general properties of such gravity, both in the linearized and the non-linear approximation. We show that generically there is an emergent (exact) diffeomoprhism invariance and the graviton is therefore ``massless" but the cosmological constant is generically non-zero.

Soft photon production and entanglement

Speaker: Nicolaos Toumbas
Institution: University of Cyprus
Time: Thursday 7 February 2019, 14:15
Venue: 2nd floor seminar room
Abstract: TBA

Emergent/Composite axions

Speaker: Pascal Anastasopoulos
Institution: University of Vienna
Time: Tuesday 12 February 2019, 14:15
Venue: 2nd floor seminar room
Abstract: Hidden theories coupled to the SM may provide emergent axions, that are composites/bound-states of the hidden fields. This is motivated by paradigms emerging from the AdS/CFT correspondence but it is a more general phenomenon. We explore the general setup and find that UV-sourced interactions of instanton densities give rise to emergent axions in the IR. We study the general properties of such axions and argue that they are generically different from both fundamental and composite axions that have been studied so far.

Effective Potential for Revolving D-branes

Speaker: Hikaru Ohta
Institution: KEK, Tsukuba
Time: Tuesday 19 February 2019, 14:15
Venue: 2nd floor seminar room
Abstract: D-branes in the superstring theory are widely used in the string phenomenology and cosmology. While it is interesting to consider the moving D-branes, we don't understand the dynamics of D-branes well enough especially when they are accelerating. In particular, it is important in the brane-world scenario to know if the stable bound states exist. As a first step, we consider a pair of D0-branes of bosonic string theory which revolve around each other in the flat spacetime. We quantize the system perturbatively with respect to the velocity of the D -branes and determine the one-loop partition function of the open string, from which we extract the short-distance behavior of the effective potential for the revolving D0-branes.

Holographic RG flows for exactly solvable model.

Speaker: Anastasia Golubtsova
Institution: BLTP JINR, Dubna, Russia
Time: Tuesday 5 March 2019, 14:15
Venue: 2nd floor seminar room
Abstract: In this seminar I will consider a gravity model with a dilaton potential given in terms of exponential functions. The form of the potential allows to reduce EOM to Toda chains and find exact solutions.The solutions can be interpreted as domain walls interpolating between different asymptotics, and as such they can have interesting applications in holography. We found solutions which interpolate between an AdS fixed point in the UV limit and a hyperscaling violating boundary in the IR region. We also find analytic black brane solutions at finite temperature. We discuss the properties of the solutions and the interpretation in terms of holographic RG flows.

Walking, weakly first-order phase transitions, and complex CFTs

Speaker: Slava Rychkov
Institution: IHES, Bures-sur-Yvette and ENS, Paris
Time: Wednesday 6 March 2019, 15:15
Venue: 2nd floor seminar room
Abstract: Most people have heard that the 2d Potts model with Q=5 states has a first order phase transition, but not everyone knows that the correlation length at this phase transition is 2500 lattice spacings. We will review "walking RG" behavior in gauge theories and connect it to Type II weak first-order phase transitions in statistical physics. Despite appearing in very different systems (QCD below the conformal window, the Potts model, deconfined criticality) these two phenomena both imply approximate scale invariance in a range of energies and have the same RG interpretation: a flow passing between pairs of fixed point at complex coupling, dubbed "complex CFTs". Observables of the real walking theory are approximately computable by perturbing the complex CFTs. The general mechanism will be illustrated by a specific and computable example: the two-dimensional Q-state Potts model with Q > 4.

Renormalization Group and Conformal Bootstrap: Friends or Foes?

Speaker: Slava Rychkov
Institution: IHES, Bures-sur-Yvette and ENS, Paris
Time: Thursday 7 March 2019, (Colloqium 17:00)
Venue: 3rd floor seminar room
Abstract: For almost 50 years Renormalization Group has been the workhorse of the theory of critical phenomena such as the liquid-gas critical point or the Curie temperature of a ferromagnet (Ising model). In the last 10 years a new method called the Conformal Bootstrap has been making significant progress. We will review the story of this friendly competition, and the main challenges faced by the two approaches.

Making the Case for Nonlocal Modifications of Gravity

Speaker: Richard Woodard
Institution: Florida University
Time: Tuesday 12 March 2019, at 14:15
Venue: 2nd floor seminar room
Abstract: TBA

Exploring greek tumulus for hidden monuments with cosmic rays

Speaker: Yannis Karyotakis
Institution: LAPP-IN2P3, CNRS, France
Time: Thursday 14 March 2019 (Colloqium 17:00)
Venue: 3rd floor Seminar Room
Abstract: Modern high energy physics experiments were initiated at the beginning of the 20th century, by experimental physicists searching to understand the ambient radioactivity and exploring particles arriving from the open sky. For many years the universe was the only source of high energy particles, and few fundamental discoveries were done, detecting cosmic particles. I will review one hundred years of observations, show some of the current experiments and comment on our present knowledge and problems. Finally I will show, how using cosmic muons we can explore the Macedonian funeral tumulus or the pyramids to detect hidden monuments or hidden rooms ! The colloquium is for a large public, not necessary familiar with particle physics.

TBA

Speaker: Kalliopi Petraki
Institution: LPTHE, Sorbonne Paris & Nikhef, Amsterdam
Time: Thursday 4 April 2019, 14:15
Venue: 2nd floor seminar room
Abstract: TBA

Conformal anomalies, C-theorems and RG Flows I

Speaker: Adam Schwimmer
Institution: Weizmann Institute of Science
Time: Tuesday 9 April 2019, 14:15 - 16:00
Venue: 2nd floor seminar room
Abstract: Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group
-Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation).
-Zamolodchikov Theorem in d=2.
-Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem.
-Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space
-More on the Structure of the Osborn Equation.

Conformal anomalies, C-theorems and RG Flows II

Speaker: Adam Schwimmer
Institution: Weizmann Institute of Science
Time: Wednesday 10 April 2019, 14:15 - 16:00
Venue: 1rst floor seminar room
Abstract: Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group
-Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation).
-Zamolodchikov Theorem in d=2.
-Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem.
-Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space
-More on the Structure of the Osborn Equation.

Conformal anomalies, C-theorems and RG Flows III

Speaker: Adam Schwimmer
Institution: Weizmann Institute of Science
Time: Thursday 11 April 2019, 13:15 - 15:00
Venue: 1rst floor seminar room
Abstract: Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group
-Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation).
-Zamolodchikov Theorem in d=2.
-Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem.
-Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space
-More on the Structure of the Osborn Equation.

The gravitational-wave astronomy: from the first results to the scientific potential of next data takings

Speaker: Matteo Barsuglia
Institution: Institute Fresnel, APC, CNRS, France
Time: Thursday 11 April 2019, 17:00
Venue: 3rd floor seminar room (Colloqium Series)
Abstract: On September 15th 2015, the two LIGO interferometers detected the first gravitational-wave, produced by the merger of two black-holes. On August 17th 2017, the coalescence of two neutron stars, localized by the network LIGO-Virgo, allowed the most important multi-messenger observation campaign of the history. Among the main results of this new gravitational-wave astronomy: the demonstration that binary black-holes exist and they can merge, the discovery of a new population of stellar mass black-holes, the link between short gamma-ray burst and mergers of neutron stars, a new measurement of the Hubble constant, the measurement of the gravitational-wave speed and the measurement of the deformability of neutron stars. After a summary of the results obtained so far, I will describe the observational plans of the next years and the challenges associated with the improvements of the gravitational-wave detectors. I will focus the last part of this seminar on the scientific potential of the new data takings, for the astrophysics of compact objects, for the cosmology and for the tests of gravity.

Cosmic Rays and Gamma-Ray Bursts

Speaker: Alvaro de Rujula
Institution: CERN
Time: Wednesday 17 April 2019, 13:15
Venue: 2nd floor seminar room
Abstract: There has been considerable recent progress in the measurements of primary cosmic rays (electrons and nuclei), as well as in the detection of the gamma rays and the lower-energy ``afterglow" associated with the binary neutron-star merger that was first seen by the gravitational wave detectors. I shall discuss these results and some of their interpretation(s).